Inkjet deposition apparatus

ABSTRACT

An inkjet deposition apparatus includes a position encoder  128  in a translation stage  116 . The position encoder provides encoder signals which are used as a clock signal for a pattern memory  136 . Ejection of droplets of a material to be printed can therefore be synchronised with the speed of movement of the translation, providing improved accuracy and speed of deposition.

[0001] The present invention relates to the deposition of solublematerials and in particular to the deposition of soluble materials usinginkjet technology.

[0002] In recent years there has been an increase in the number ofproducts which require, as part of their fabrication process, thedeposition of organic or inorganic soluble or dispersible materials suchas polymers, dyes, colloid materials and the like on solid surfaces. Oneexample of these products is an organic polymer electroluminescentdisplay device. An organic polymer electroluminescent display devicerequires the deposition of soluble polymers into predefined patterns ona solid substrate in order to provide the light emitting pixels of thedisplay device. Further examples include the deposition of materials forforming organic polymer thin film transistors (TFTs) on a substrate andinterconnects between chips assembled on the substrate using fluidicself assembly (FSA). The substrate may, for example, be formed of glass,plastics or silicon.

[0003] Typically, the substrate is a rigid substrate, thereby providinga rigid display device. However, products comprising flexible displays,which may be rolled or folded, are increasingly sought after, inparticular where a large display is required. Such flexible displaysprovide substantially improved weight and handling characteristics andare less likely to fail due to shock during installation of the displaydevice or use of the display device. In addition, relatively smalldisplay devices comprising a large display area may be convenientlyprovided.

[0004] In the manufacture of semiconductor display devices, includinglight emitting diode (LED) displays, it has been conventional to usephotolithographic techniques. However, photolithographic techniques arerelatively complex, time consuming and costly to implement. In addition,photolithographic techniques are not readily suitable for use in thefabrication of display devices incorporating soluble organic polymermaterials. Concerns relating to the fabrication of the organic polymerpixels have, to some extent, hindered the development of products suchas electroluminescent display devices incorporating such materials toact as the light emitting pixel elements.

[0005] The use of etch masks, such as photo masks for photolithographyor metal shadow masks for patterning by evaporation deposition, is wellknown in conventional fabrication techniques. Hence, these processeswill not be described in detail in the context of the present invention.However, such conventional fabrication techniques present severe processconcerns for a number of practical applications including large scaledisplay devices. Indeed, the etching and deposition of relatively longbut extremely narrow lines has, for a long period of time, presentedsevere fabrication difficulties as it is very difficult to producemechanically robust masks which will provide the required definition inthe finished product. For example, a metal shadow mask for evaporationdeposition for a large scale display device will inevitably exhibit somesagging or bowing in the central unsupported portion of the mask. Thisleads to an uneven distance between the mask and the substrate at theedge and the centre of the substrate respectively, thereby giving riseto uneven width and thickness of the deposited lines which can adverselyaffect the quality of the displayed image.

[0006] Consequently, it has been proposed to use inkjet technology todeposit the soluble organic polymers in the fabrication of, for example,electroluminescent display devices. Inkjet technology is, by definition,ideally suited to the deposition of such soluble or dispersiblematerials. It is a fast and inexpensive technique. In contrast toalternative techniques such as spin coating or vapour deposition, itinstantly provides patterning without the need for an etch step incombination with a lithographic technique. However, the deposition ofthe soluble organic materials onto the solid surface using inkjettechnology differs from the conventional use of the technology, todeposit ink on paper, and a number of difficulties are encountered. Inparticular, there is a primary requirement in a display device foruniformity of light output and uniformity of electrical characteristics.There are also spatial limitations imposed in device fabrication. Assuch, there is the non-trivial problem to provide very accuratedeposition of the soluble polymers onto the substrate from the ink-jetprint head. This is particularly so for colour displays as respectivepolymers providing red, green and blue light emissions are required tobe deposited at each pixel of the display.

[0007] To assist the deposition of the soluble materials it has beenproposed to provide the substrate with a layer which includes a patternof wall structures defined in a de-wetting material so as to provide anarray of wells or elongate trenches, bounded by the wall structures, forreceiving the material to be deposited. Such a patterned substrate willbe referred to hereinafter as a bank structure. When organic polymers insolution are deposited into the wells, the difference in the wettabilityof the organic polymer solutions and the bank structure material causesthe solution to self align into the wells provided on the substratesurface.

[0008] However, it is still necessary to deposit the droplets of organicpolymer material in substantial alignment with the wells in the bankstructure. Even when such a bank structure is used, the depositedorganic polymer solution adheres to some extent to the walls of thematerial defining the wells. This causes the central area of eachdeposited droplet to have, at best, a thin coating of depositedmaterial, perhaps as low as 10% of the material in comparison to thematerial deposited at the walls of the bank structure. The depositedpolymer material at the centre of the wells acts as the active lightemissive material in the display device. If the polymer material is notdeposited in accurate alignment with the wells, the material will bedistributed unevenly, and therefore the amount and thickness of theactive light emissive material can be further reduced. This thinning ofthe active light emissive material is of serious concern because thecurrent passing through the material in use of the display is increasedwhich reduces the life expectancy and the efficiency of the lightemissive devices of the display. This thinning of the deposited polymermaterial will also vary from pixel to pixel if deposition alignment isnot accurately controlled. This gives rise to a variation in the lightemission performance of the organic polymer material from pixel to pixelbecause the LEDs constituted by the organic material are current drivendevices and, as stated above, the current passing through the depositedpolymer material will increase with any decrease in the thickness of thedeposited material.

[0009] This performance variation from pixel to pixel gives rise tonon-uniformity in the displayed image, which degrades the quality of thedisplayed image. This degradation of image quality is in addition to thereduction in operating efficiency and working life expectancy of theLEDs of the display. It can be seen therefore that accurate depositionof the polymer materials is essential to provide good image quality anda display device of acceptable efficiency and durability, irrespectiveof whether a bank structure is provided.

[0010] There are two main types of inkjet head. One type uses a thermalprint head and these are commonly known as bubble jet heads. The secondtype uses a piezoelectric print head where a piezoelectric device islocated behind a diaphragm in communication with a reservoir. In thissecond type of inkjet head the piezoelectric device is energised and thediaphragm deflects to pressurise the reservoir, forcing the liquidcontained in the reservoir, in this case the polymer material insolution to provide the light emissive pixels for a display, out througha nozzle as a fine droplet of the polymer material. With either type ofprint head, the nozzle has a very small outlet orifice, typically of adiameter of about 30 microns. The organic polymers are usually dissolvedin a relatively volatile organic solvent so that they can be depositedin solution.

[0011] During deposition, the inkjet print head is maintained as closeas possible to the substrate. Usually, the inkjet print head is arrangedat a separation of about 0.5 mm to 1.0 mm above the substrate. However,in inkjet printing the droplets have a flight speed typically in therange of 2 to 10 ms⁻¹. The relative speed between the substrate andprint head is typically in the range of 0.1 to 1 ms⁻¹. Assuming adroplet speed of about 5 ms⁻¹ and a separation of 1 mm between theinkjet head and substrate, the time taken for an ejected droplet toreach the substrate is about 0.2 milliseconds. If the print head has atransverse speed of 0.1 ms⁻¹ relative to the deposition substrate, anoffset of 20 μm will be created between the ejection point and theactual deposition point on the substrate. This offset is regular andequal for all nozzles of the inkjet print head. For conventionalprinting, in which case the substrate is paper, which is the normal useof this technology, this offset is not problematical because it is thesame over the entire printed image and such a small offset in theposition of the printed image on the paper is not discernible to aperson viewing the printed image.

[0012] However, it will be appreciated that offsets of the order 20′ μmare significant when printing electronic, opto-electronic or opticaldevices such as colour filters on a substrate. For example, where anorganic polymer TFT is to be printed on the substrate it is desirable tomaintain a channel length between the source and drain as small aspossible, and preferably less than 20 μm. Similarly, in a colourelectroluminescent device, it is necessary to provide a droplet of eachof three different organic materials, as well as to deposit electrodesfor each droplet, within one pixel area. Hence, to improve the accuracyof deposition for printing electronic devices, a ‘step and drop’technique, as described in more detail below, is usually adopted.

[0013]FIG. 1 shows a conventional inkjet deposition machine 100 for arigid substrate comprising a base 102 supporting a pair of uprightcolumns 104. The columns 104 support a transverse beam 106 upon which ismounted a carrier 108 supporting an inkjet print head 110. The base 102also supports a platen 112 upon which may be mounted a substrate 114,which is typically glass and currently has a typical maximum size of 40cm×50 cm. The platen 112 is mounted from the base 102 via a computercontrolled motorised translation stage for effecting movement of theplaten 112 both in a transverse and a longitudinal direction relative tothe inkjet print head, as shown by the axes X and Y in FIG. 1. As themovement of the platen 112, and hence the substrate 114 relative to theinkjet head 110 is under computer control, arbitrary patterns may beprinted onto the substrate by ejecting appropriate materials from theinkjet head 110. The computer control is further used to control theselection and driving of the nozzles and a camera may be used to viewthe substrate during printing.

[0014] Movement of the platen 112, especially if the platen is for alarge substrate, gives rise to considerable momentum and therebynecessitates the provision of a large and usually massive support orbase 102. The considerable momentum of the platen 112 exacerbates theproblem of backlash. Backlash, which is known and problematic even inconventional printing on paper, is caused by reversing the direction ofthe translation stage 116. This reversal of direction causes anerroneous position of the print head relative to the substrate.Generally, the faster the reversal of direction, the greater the error.Accordingly, in order to calculate the correct relative position of thetranslation stage relative to the print head, it is usually necessaryfor the control system to read encoding marks for the translationmechanism after the direction of printing has been reversed but beforeprinting recommences.

[0015] However, even if encoding marks for the translation mechanism areread after the direction of printing has been reversed, subsequentlydeposited droplets with the translation stage moving in the reversedirection will not be aligned with droplets deposited while thetranslation stage is moved in the forward direction. This is because thecontrol system calculates the position of the translation mechanism withrespect to a reference point different to that used for the forwarddirection.

[0016] To avoid this problem of asymmetric deposition, droplets may bedeposited when the translation mechanism is moved in one direction only,so that the control system calculates the position of the translationmechanism with respect to a single reference point. However, depositingdroplets in a single direction considerably lowers the deposition speedand hence significantly increases the time required to fabricate thedevices.

[0017] It has been proposed to provide a mechanism for translating theprint head 110 along the beam 106 disposed horizontally over thestationary substrate 114. However, the beam 106, being a physicalstructure, bends very slightly under gravitational forces. Thus, thecentre part of the beam 106 will substantially maintain its horizontaldisposition so that a droplet deposited with the print head 110positioned over a central location of the substrate 114 will maintain aflight path perpendicular to the substrate 114. However, as the printhead 110 is translated away from this central part of the beam 106, itwill no longer be supported truly horizontally over the substrate 114 sothe flight path at this second position will no longer be perpendicularto the substrate 114. Hence, if the print head is moved by X cm alongthe beam 106, this can give rise to a variation in deposition point ofX+α at the substrate 114, where a is the additional variable offsetcaused by the slight bending of the beam 106. Of course, offset aincreases as X increases.

[0018]FIG. 2 illustrates the operation of the inkjet machine shown inFIG. 1.

[0019] The inkjet machine 100 is controlled from a computer 118, wherethe pattern and printing coordinates of the device to be printed in thesubstrate 114 are defined. A command to move the translation stage 116is sent from the computer 118 to a motion controller 120. When thetranslation stage reaches a certain position, the motion controller 120sends a ‘ready’ signal to the computer 118 and a trigger pulse is thensent by the computer to a waveform generator 122. This waveformgenerator provides drive signals which are used to drive ink-jet printhead 110 via a power amplifier 124. When printing a device with themachine 100, the translation stage is normally programmed to move to arequired position, and when this position is reached, the translationstage stops and the inkjet head 110 is programmed to print one, or anumber of drops of a material to be used to print the pattern. Thetranslation stage is then moved to another coordinate under programcontrol, and then one or a number of drops are again ejected from theprint head. The printing time using this ‘step and drop’ technique isrelatively long because the majority of the fabrication time is consumedby waiting for the translation stage to stop. To be able to print acontinuous line for example, it is possible for the frequency of thedrive signals which are output from the waveform generator 122 to be setindependently of the motion of the translation stage 116 but in allcases, the computer controls the operation of the inkjet headindependently of the control of the motorised translation stage.

[0020] However, the space between each droplet in the printed line isdetermined by both the frequency of the pulses of the driving waveformand the velocity of the translation stage. Therefore, extremely accuratematching of these two parameters is required in order to achieveaccurate printing and this is extremely difficult to achieve inpractice. It is more usual in the printing of electronic devices toarrange for the translation mechanism to move the substrate relative tothe print head but because there is no correlation between the actualposition of the translation stage and the timing of droplet ejection,printing errors which are unsatifactory for device fabrication continueto occur.

[0021] The distinction between a standard inkjet printer used forprinting documents and an inkjet machine for printing electronic devicesis that in the case of printing a document, there may be an error in theabsolute position of the droplets, but since the space between eachdroplet is relative, the printed image will appear correct to the eye ofa viewer whereas, for an electronic device, the absolute position of theprinting must be maintained throughout the whole area of printing of thedevice in order to obtain devices of the required performance andquality.

[0022] For the current inkjet machine as outlined above, the translationstage 116 comprises a stepping motor stage. Such a stage has a leadscrew which rotates according to the frequency and number of commandpulses it receives from the motion controller. This lead screw usuallyhas some errors; i.e. it may for example have a periodic fluctuation inthe screw pitch, which can give rise to a periodic error in thetranslation distance, which in turn gives rise to errors in thepatterning of the device. The position of the stage is not continuouslymonitored as it moves; the position is set by coordinates received bythe motion controller 120 from the computer 118 and it is assumed thatthe actual position reached by the translation stage 116 will be theposition as instructed by the stored coordinates. It is also expectedthat the translation stage will have reached a stationary condition atthe required coordinates when the droplet or droplets are ejected fromthe inkjet head 110. However, because of the positional errors in thetranslation stage, printing may be made when the stage is still inmotion. If either of the above conditions occur, no matter how preciselythe output signals of the waveform generator are matched to the velocityor stored position of the translation stage, there will be an error inthe position of the printing. The only way an error can be compensatedis by moving the translation stage by small amounts to the correctposition, and effecting printing statically at the corrected position.This process can be particularly burdensome as the corrected positionneeds to be determined by viewing the device being printed with amicroscope which must be incorporated into the inkjet machine. This isparticularly burdensome and leads to a significant increase in the costof fabricating devices.

[0023] The time required to fabricate certain electronic devices, suchas organic LED displays, can be a crucial factor in the resultingdisplay quality exhibited by the display. One reason for this is thatthe organic polymer materials can degrade if exposed for too long to theordinary atmosphere during fabrication. Hence, an inkjet machine whichis able to not only improve the accuracy of material deposition but isalso able to achieve such improved deposition in a shorter fabricationtime is highly desirable and particularly advantageous.

[0024] The present invention seeks to provide therefore an improved formof inkjet machine in which both the accuracy and speed of printing ofthe materials to be deposited are enhanced in comparison to the knownforms of inkjet machine.

[0025] According to a first aspect of the present invention there isprovided an inkjet machine comprising means for providing drive signalsto an inkjet print head, the drive signals being arranged to causeejection of one or more droplets of material to be printed from a nozzleof the inkjet print head, a translation stage for providing relativemovement between a substrate to be printed with the material and theinkjet print head, a monitoring unit for monitoring the position of thetranslation stage and control means for controlling the provision of thedrive signals in dependence upon the monitored position of thetranslation stage.

[0026] Preferably, the translation stage is arranged to move thesubstrate relative to the ink-jet print head.

[0027] In a preferred embodiment, the monitoring unit comprises aposition encoder, which may comprise an optical encoder, for providingan encoder signal having a frequency dependent upon the speed ofmovement of the translation stage.

[0028] The encoder signal may be arranged to control the timing of theprovision of the drive signals to the inkjet print head duringtranslation of the substrate relative to the head corresponding to aspatial resolution in the range of from about 0.1 to about 10 micronsbetween two successive droplets deposited from the inkjet head.

[0029] Advantageously, the timing of the provision the drive signalscorresponds to a movement of 0.2 microns of the translation stage.

[0030] The inkjet machine may also be provided with a clock source forcontrolling the provision of the drive signals from the waveformgenerator when there is no movement of the translation stage and theinkjet print head is positioned outside of an area to be printed on thesubstrate.

[0031] By using a translation stage with a feedback system, the positionof the stage is continuously monitored, and the timing of the drivesignals from the waveform generator is automatically controlled by thetranslation speed of the translation stage. The result of using such asystem with position registration is that the timing of the ejection ofthe material being printed is determined by the actual position of thestage, and not by a time based calculation which is based upon anassumed position for the translation stage, as in the case for currentinkjet machines. Also, any errors in the manufacturing tolerances of thelead screw of the translation stage can be compensated for, because thesystem continuously corrects for any unpredictable fluctuations in thevelocity at which the translation stage is moved.

[0032] According to a second aspect of the present invention there isprovided a method of inkjet printing comprising monitoring the positionof a translation stage for providing relative movement between asubstrate to be printed and an inkjet print head, and controlling theprovision of drive signals arranged to cause ejection of one or moredroplets of material from a nozzle of the inkjet print head independence upon the monitored position of the translation stage.

[0033] In a preferred method, the translation stage is arranged toprovide movement of the substrate relative to the inkjet print head.

[0034] The method may comprise generating an encoder signal having afrequency dependent upon the speed of movement of the translation stageand using the encoder signal to control the provision of the drivesignals.

[0035] An optical encoder may, advantageously, be used to generate theencoder signal.

[0036] In a preferred form of the method, the encoder signal is arrangedto control the timing of the provision of the drive signals to theinkjet print head such that the translation stage provides relativemovement between the substrate and the inkjet print head of from about0.1 to about 10 microns between ejection of two successive droplets fromthe inkjet head.

[0037] Preferably, the timing of the provision of the drive signalsprovides about 0.2 microns of spatial resolution between two successivedroplets deposited from the inkjet head.

[0038] The method of the present invention may also comprise selecting aclock signal from a clock source for controlling the provision of thedrive signals to the inkjet print head when there is no movement of thetranslation stage and the inkjet print head is positioned outside of anarea to be printed on the substrate.

[0039] According to a third aspect of the present invention there isprovided an electronic, opto-electronic, optical or sensor devicemanufactured using an inkjet machine according to the first aspect or amethod of inkjet printing according to the second aspect.

[0040] Embodiments of the present invention will now be described by wayof further example only and with reference to the accompanying drawings,in which:

[0041]FIG. 1 is a schematic representation of a prior art inkjetdeposition apparatus;

[0042]FIG. 2 is a schematic block diagram of the control system forcontrolling the operation of the inkjet head and the motion of thetranslation stage for the inkjet deposition apparatus shown in FIG. 1;

[0043]FIG. 3 is a schematic block diagram of a control system of aninkjet deposition apparatus according to the present invention;

[0044]FIG. 4 shows waveform diagrams for the control system illustratedin FIG. 3;

[0045]FIG. 5 shows a block diagram of an electrooptic device;

[0046]FIG. 6 is a schematic view of a mobile personal computerincorporating a display device fabricated by apparatus in accordancewith the present invention;

[0047]FIG. 7 is a schematic view of a mobile telephone incorporating adisplay device fabricated by apparatus in accordance with the presentinvention; and

[0048]FIG. 8 is a schematic view of a digital camera incorporating adisplay device fabricated by apparatus in accordance with the presentinvention.

[0049] Referring to FIG. 2, which shows a known form of inkjetdeposition apparatus, the computer 118 defines the pattern and printingcoordinates of the device to be printed on the substrate 114 by theinkjet head 110. The inkjet head 110 includes a matrix array of nozzles(not shown), each for ejecting the droplets of the material to beprinted. The pattern information stored in the computer 118 is used togenerate nozzle selection signals which are fed to the inkjet head 110.These nozzle selection signals determine which of the nozzles of thearray of nozzles are to be used to eject the material for printing atany part of the pattern for the device being printed. The computer 118,from the pattern and printing coordinates, controls the motioncontroller 120 which outputs motion command signals which cause themotorised translation stage to take up a desired position under theinkjet print head.

[0050] However, it can be clearly seen from FIG. 2 that there is nofeedback from the translation stage to the other parts of the system sothe system operation is based on the assumption that the motorisedtranslation stage can move at a predefined velocity and to a predefinedpositional accuracy to ensure that, when the driving pulses from thewaveform generator 122 are received by the inkjet head, the ejecteddroplets from the nozzles selected by the nozzle selection signals aredeposited at the desired coordinates on the substrate 14.

[0051]FIG. 3 shows the control system for an inkjet deposition machineof the present invention and like reference numerals are used in FIG. 3to describe like parts of the system shown in FIG. 2. A computer 118provides master control of the system and, as with the system shown inFIG. 2, nozzle selection signals are provided to the inkjet head toselect those nozzles from which ejection of the material for printing isto occur. The ink-jet deposition apparatus also includes a waveformgenerator (not shown in FIG. 3) for supplying the driving pulses to theinkjet head. In the above respects therefore the ink-jet depositionapparatus is similar to the apparatus shown in FIG. 2.

[0052] A principal difference with the inkjet apparatus of the presentinvention is that the waveform generator is driven by a data generator126 instead of being driven directly from the computer 118. The datagenerator 126 is arranged to receive an encoder signal from a positionencoder 128 which is incorporated into the motorised translation stage116. The encoder signal from the position encoder 128 is used as anexternal clock signal for a pattern memory 130 of the data generator126. Hence, the inkjet apparatus provides synchronisation between themotion of the translation stage 116 and the pattern data held in thepattern memory. The timing at which the inkjet head is driven by thedriving pulses from the waveform generator is therefore determined bythe velocity and actual sensed position of the translation stage 116.

[0053] As with the inkjet apparatus shown in FIG. 2, the computer 118 isprogrammed with the pattern data of the device to be printed. Inoperation of the apparatus, the pattern data is sent by the computer 118to the data generator 126, where it is stored in the pattern memory 130.The nozzles to be used for printing of the pattern are then selected bythe provision by the computer 118 of the nozzle selection signals to theinkjet head. The computer 118 also provides a motion command or drivingsignal to an actuator 132 in the translation stage 116 via a stagecontrol circuit 134 which causes the translation stage to move to thedesired coordinates in relation to the nozzles of the inkjet head asrequired by the pattern data. Preferably, the actuator 32 comprises a DCservomotor, which may be a linear or rotary type motor.

[0054] The translation stage, however, includes the position encoder128, which may for example be an optical or a magnetic encoder, thatprovides an encoder signal which is fed to the stage control circuit 134and the data generator 126. By using the encoder signal in a feedbacksystem to the stage control circuit, the driving signal fed to thetranslation stage can be controlled to ensure that the translation stage116 is moved relative to the print head with the required velocity andto the required coordinates. Hence, the system is able to compensate forany periodic fluctuations which may be present in the lead screw orother parts of the actuator used to effect motion to the translationstage 116.

[0055] The encoder signal is also fed to the data generator 126 via aswitch 136 where it acts as a clock signal for the pattern memory 130.In this manner, the output signal from the data generator 126, whichacts as a trigger signal for the waveform generator, is synchronisedwith the actual motion of the translation stage 116. Hence, theprovision of the drive signals from the waveform generator, which causethe ejection of droplets of the material to be printed from the nozzlesof the inkjet head, are controlled in dependence upon the position ofthe translation stage 116.

[0056] The translation stage is programmed by the computer 118 withposition coordinates for the pattern, required acceleration and velocityof movement and the data generator 126 is actually clocked when thetranslation stage moves through the provision of the encoder signal fromthe position encoder 128. Thus, printing of the electronic device on thesubstrate can be made at any time, including when the translation stage116 is accelerating, decelerating or moving at constant speed, therebydecreasing significantly the time required to fabricate the electronicdevice on the substrate.

[0057] Furthermore, because the pattern memory 130 is synchronised withthe movement of the translation stage 116, extremely accurate printingof the required pattern can be achieved since the ejection of thematerial for printing from the inkjet head is controlled by the actualposition of the translation stage 116, as sensed by the position encoder128, and not by a time based system as in the independent waveformtriggering of the prior art system shown in FIG. 2. Preferably, theposition encoder 128 provides encoder signals having a frequency suchthat the pattern memory 130 is clocked with a cycle corresponding tofrom about 0.1 to about 10 microns of travel of the translation stage116. For the printing of most devices a cycle corresponding to 0.2microns of travel of the translation stage has been found to beparticularly beneficial.

[0058] The signal timing for operation of the inkjet apparatus can beseen in FIG. 4.

[0059] Movement of the translation stage 116 is started by the provisionby the computer 118 of a start movement trigger pulse 200 to the stagecontrol 134. Upon receipt of the pulse 200 the stage control 134provides a current based driving signal 202 to the actuator 132 of thetranslation stage 116. The driving signal 202 is arranged to ramp upquickly from zero to a level L₁ and the level L₁ is held for a shortperiod of time so as to provide rapid acceleration of the translationstage 116. The driving signal 202 is then reduced from level L₁ to areduced level, shown as level L₂ in FIG. 4, to provide a constantvelocity to the translation stage. The level L₂ of the driving signal ismaintained until a negative current, shown as level L₃ in FIG. 4, isapplied to the actuator so as to rapidly decelerate the translationstage 116. Hence, over a translation cycle, the translation stage 116 isaccelerated during the period A to B, maintains a steady velocity duringthe period B to C and is decelerated during the period C to D. Thevelocity of the translation stage is therefore as shown by plot 204shown in FIG. 4.

[0060] The output signal of the position encoder is shown as encodersignal 206 in FIG. 4 and is in the form of a square wave pulse train. Itcan be seen from the signal 206 that the frequency of the pulse train isproportional to the velocity of the translation stage. Hence, as thetranslation stage is accelerated during the period A to B, the encodersignal 206 increases in frequency to reach a steady state pulserepetition frequency which is maintained during the period B to C, whenthe translation stage is moved at a steady state constant velocity, andreduces in frequency during the deceleration period C to D of thetranslation stage 116. Hence, each pulse of the encoder signalrepresents a fixed amount of movement of the translation stage; 0.2microns in the embodiment described.

[0061] The pattern of the printing required from the inkjet head isstored as a sequence of data in the memory area of the data generator126. The pattern data is represented by data elements D₁ to D_(n) inFIG. 4. Each element corresponds to one period in the encoder signal,and may be programmed to give a high or a low output as shown in thefigure. It is possible to program the data elements such that the outputfrom the data generator gives a pulse during any part of the velocityprofile of the translation stage. During printing of the device theswitch 136 of the data generator is arranged so that the encoder signalfrom the position encoder 128 is input to function as a clock signal forthe pattern memory 130. For each 0.2 microns of movement of thetranslation stage 116, the position encoder 128 provides an encodersignal in the form of one of the pulses of the pulse train 206 shown inFIG. 4. Element D3 corresponds to the third pulse of the pulse train 206from the position encoder 128; namely, at the time when the translationstage has moved through 0.6 microns from its initial rest position. Thisthird pulse from the position encoder acts as a clock pulse for thepattern memory 130, which provides an output signal from the datagenerator 126 via an output circuit 138. Such an output signal providedfrom the data generator 126 acts as a trigger for the waveformgenerator. The output signal from the data generator 126 is therefore inthe form of a pulse train 208, with the spacing between pulses 210 ofthe pulse train being determined by the pattern data stored in thepattern memory and the pulses of the encoder signal 206 output from theposition encoder 128, which trigger the data generator to output thepulses 210.

[0062] The pulses 210 from the data generator are fed to and act asclock or trigger pulses for the waveform generator, which provides adriving pulse 212 to the inkjet print head each time that a pulse 210 isreceived. It can be seen therefore from the waveform and timing diagramsshown in FIG. 4 that the provision of the driving pulses 212 to theinkjet head, which cause the ejection of the droplets of material to beprinted from the head, is synchronised with the speed of the translationstage 116. Hence, irrespective of whether the translation stage isaccelerating, decelerating or moving at a constant speed, the dropletsof material to be printed are ejected at the correct co-ordinates ontothe substrate. This is also the case when a variation in the speed ofthe translation stage takes place, such as may occur as a result of aperiodic variation in the pitch of the lead screw used to physicallydrive the translation stage 116.

[0063] During or between printing of devices by the inkjet apparatusshown in FIG. 3, there may be periods of time when the inkjet head isnot used for printing a device and the ink-jet head is then positionedat an idling position outside of the device area on the substrate.However, to prevent clogging of the nozzles of the inkjet head duringthese idling periods it is necessary to periodically eject material fromthe nozzles of the inkjet head. During such idling periods, thetranslation stage is stationary and hence an encoder signal from theposition encoder 128 is not present to use as a clock pulse for thepattern memory 130. Hence, there is no output signal from the datagenerator and the waveform generator does not therefore provide thedriving pulses to the inkjet print head.

[0064] Therefore, upon commencement of an idling period the switch 136is operated to couple a clock generator 140 to the pattern memory. Theclock generator produces a stream of clock pulses which substitute forthe encoder signals provided during translation of the translation stage116. Hence, the pattern generator outputs a stream of trigger pulses tothe waveform generator in synchronism with the clock pulses from theclock generator 140. Clogging of the nozzles of the inkjet head duringthe idling periods is therefore avoided. Such a procedure may also beused for periodic cleaning of the nozzles.

[0065] The translation stage 116 can move the substrate in both an X anda Y axis relative to the inkjet head and comprises therefore respectivestages with respective lead screws for the X and Y axes.

[0066] The system of the present invention can also be used to correctfor errors in the displacement of the X and Y stages. For instance, anover or under shoot of translation length of either stage can becorrected by programming the computer 118 with a correction for theco-ordinates of the device being printed. This error may occur in bothaxes X and Y, thus the new co-ordinate system is applied to cover thewhole area of that device in both axes. Various alignment marks can beobserved on a device, and so by programming the stages to move to theseco-ordinates, it is possible to observe the error in the position of thestages over relatively large distances across the device. For example,along the X axis say, the stage can be programmed to move from one markto another, and by rotation of the device it is possible to compensatefor an error in the position of the device on the stage. However, thelength of travel may be also be determined as being too long or tooshort along this axis. This error can be compensated for by programminga correction factor into the travel length command for this single axis.

[0067] Ideally, the construction angle between the axes X and Y of thetranslation stage must be exactly 90 degrees. However, in practice, thisideal construction angle is usually not achieved due to manufacturingtolerances. Hence, when the stages are programmed to move to a certainco-ordinate there will be an offset error. The system may also beprogrammed to compensate for such errors in the construction anglebetween the two axes.

[0068]FIG. 5 is a block diagram illustrating an active matrix typedisplay device (or apparatus) incorporating electro-optical elements,such as organic electroluminescent elements as a preferred example ofthe electro-optical devices, and an addressing scheme which may befabricated using the method or apparatus of the present invention. Inthe display device 200 shown in this figure, a plurality of scanninglines “gate”, a plurality of data lines “sig” extending in a directionthat intersects the direction in which the scanning lines “gate” extend,a plurality of common power supply lines “corn” extending substantiallyparallel to the data lines “sig”, and a plurality of pixels 201 locatedat the intersections of the data lines “sig” and the scanning lines“gate” which are formed above a substrate.

[0069] Each pixel 201 comprises a first TFT 202, to which a scanningsignal is supplied to the gate electrode through the scanning gate, aholding capacitor “cap” which holds an image signal supplied from thedata line “sig” via the first TFT 202, a second TFT 203 in which theimage signal held by the holding capacitor “cap” is supplied to the gateelectrode (a second gate electrode), and an electro-optical element 204such as an electroluminescent element (indicated as a resistance) intowhich the driving current flows from the common power supply line “com”when the element 204 is' electrically connected to the common powersupply line “com” through the second TFT 203. The scanning lines “gate”are connected to a first driver circuit 205 and the data lines “sig” areconnected to a second driver circuit 206. At least one of the firstcircuit 205 and the second circuit 205 can be preferably formed abovethe substrate above which the first TFTs 202 and the second TFTs 203 areformed. The TFT array(s) manufactured by the methods according to thepresent invention can be preferably applied to at least one of an arrayof the first TFTs 202 and the second TFTs 203, the first driver circuit205, and the second driver circuit 206.

[0070] The present invention may therefore be used to fabricate displaysand other devices which are to be incorporated in many types ofequipment such as mobile displays e.g. mobile phones, laptop personalcomputers, DVD players, cameras, field equipment; portable displays suchas desktop computers, CCTV or photo albums; instrument panels such asvehicle or aircraft instrument panels; or industrial displays such ascontrol room equipment displays. In other words, an electro-opticaldevice or display to which the TFT array(s) manufactured by theapparatus of the present invention is (are) applied as noted above canbe incorporated in the many types of equipment, as exemplified above.

[0071] Various electronic apparatuses using electro-optical displaydevices fabricated by the apparatus of the present invention will now bedescribed.

[0072] <1: Mobile Computer>

[0073] An example in which the display device fabricated in accordancewith one of the above embodiments is applied to a mobile personalcomputer will now be described.

[0074]FIG. 6 is an isometric view illustrating the configuration of thispersonal computer. In the drawing, the personal computer 1100 isprovided with a body 1104 including a keyboard 1102 and a display unit1106. The display unit 1106 is implemented using a display panelfabricated according to the patterning method of the present invention,as described above.

[0075] <2: Portable Phone>

[0076] Next, an example in which the display device is applied to adisplay section of a portable phone will be described. FIG. 7 is anisometric view illustrating the configuration of the portable phone. Inthe drawing, the portable phone 1200 is provided with a plurality ofoperation keys 1202, an earpiece 1204, a mouthpiece 1206, and a displaypanel 100. This display panel 100 is implemented using a display devicefabricated in accordance with the method of the present invention, asdescribed above.

[0077] <3: Digital Still Camera>

[0078] Next, a digital still camera using an OEL display device as afinder will be described. FIG. 8 is an isometric view illustrating theconfiguration of the digital still camera and the connection to externaldevices in brief.

[0079] Typical cameras use sensitized films having light sensitivecoatings and record optical images of objects by causing a chemicalchange in the light sensitive coatings, whereas the digital still camera1300 generates imaging signals from the optical image of an object byphotoelectric conversion using, for example, a charge coupled device(CCD). The digital still camera 1300 is provided with an OEL element 100at the back face of a case 1302 to perform display based on the imagingsignals from the CCD. Thus, the display panel 100 functions as a finderfor displaying the object. A photo acceptance unit 1304 includingoptical lenses and the CCD is provided at the front side (behind in thedrawing) of the case 1302.

[0080] When a cameraman determines the object image displayed in the OELelement panel 100 and releases the shutter, the image signals from theCCD are transmitted and stored to memories in a circuit board 1308. Inthe digital still camera 1300, video signal output terminals 1312 andinput/output terminals 1314 for data communication are provided on aside of the case 1302. As shown in the drawing, a television monitor1430 and a personal computer 1440 are connected to the video signalterminals 1312 and the input/output terminals 1314, respectively, ifnecessary. The imaging signals stored in the memories of the circuitboard 1308 are output to the television monitor 1430 and the personalcomputer 1440, by a given operation.

[0081] Examples of electronic apparatuses, other than the personalcomputer shown in FIG. 6, the portable phone shown in FIG. 7, and thedigital still camera shown in FIG. 8, include OEL element televisionsets, view-finder-type and monitoring-type video tape recorders, vehiclenavigation and instrumentation systems, pagers, electronic notebooks,portable calculators, word processors, workstations, TV telephones,point-of-sales system (POS) terminals, and devices provided with touchpanels. Of course, OEL devices fabricated using the apparatus of thepresent invention can be applied not only to display sections of theseelectronic apparatuses but also to any other form of apparatus whichincorporates a display section.

[0082] Furthermore, the display devices fabricated in accordance withthe present invention are also suitable for a screen-type large areatelevision which is very thin, flexible and light in weight. It ispossible therefore to paste or hang such large area television on awall. The flexible television can, if required, be conveniently rolledup when it is not used.

[0083] Printed circuit boards may also be fabricated using the apparatusof the present invention. Conventional printed circuit boards arefabricated by photolithographic and etching techniques, which increasethe manufacturing cost, even though they are a more cost-oriented devicethan other microelectronics devices, such as IC chips or passivedevices. High-resolution patterning is also required to achievehigh-density packaging. High-resolution interconnections on a board canbe easily and reliably be achieved using the present invention.

[0084] Colour filters for colour display applications may also beprovided using the present invention. Droplets of liquid containing dyeor pigment are deposited accurately onto selected regions of asubstrate. A matrix format is frequently used with the droplets inextremely close proximity to each other. In situ viewing can thereforeprove to be extremely advantageous. After drying, the dye or pigments inthe droplets act as filter layers.

[0085] DNA sensor array chips may also be provided using the presentinvention. Solutions containing different DNAs are deposited onto anarray of receiving sites separated by small gaps as provided by thechips.

[0086] The aforegoing description has been given by way of example onlyand it will be appreciated by a person skilled in the art thatmodifications can be made without departing from the scope of thepresent invention.

[0087] For example, a separate controller, which is responsive to theencoding signals from the encoder, may be provided for controlling theprovision of the drive signals from the monitored position of thetranslation stage. Furthermore, the present invention has been describedwith reference to inkjet printing machines in general and withoutreference to any particular type or form of substrate. However, it isapparent from the above description that the present invention canprovide particular benefits in the fabrication of devices, asexemplified above, and thus is particularly suited to printing onpre-patterned substrates which can carry pre-patterns in the form, forexample, of electrode pre-patterns or one or more pre-patterns of wallstructures defined in a material having a de-wetting characteristic forthe material to be printed.

1. An inkjet machine comprising means for providing drive signals to aninkjet print head, the drive signals being arranged to cause ejection ofone or more droplets of material to be printed from a nozzle of theinkjet print head, a translation stage for providing relative movementbetween a substrate to be printed with the material and the inkjet printhead, a monitoring unit for monitoring the position of the translationstage and control means for controlling the provision of the drivesignal in dependence upon the monitored position of the translationstage.
 2. An inkjet machine as claimed in claim 1, wherein thetranslation stage is arranged to move the substrate relative to theinkjet print head.
 3. An inkjet machine as claimed in claim 1 or 2,wherein the monitoring unit comprises a position encoder for providingan encoder signal having a frequency dependent upon the speed ofmovement of the translation stage.
 4. An inkjet machine as claimed inclaim 3, wherein the position encoder comprises an optical encoder. 5.An inkjet machine wherein the encoder signal is arranged to control thetiming of the provision of the drive signals to the inkjet print headduring translation of the substrate relative to the head correspondingto a spatial resolution in the range of from about 0.1 to about 10microns between two successive droplets deposited from the inkjet head.6. An inkjet machine as claimed in claim 5 wherein the timing of theprovision of the drive signals provides about 0.2 microns of spatialresolution between two successive droplets deposited from the inkjethead.
 7. An inkjet machine as claimed in any one of the preceding claimscomprising a clock source for controlling the provision of the drivesignals from the waveform generator when there is no movement of thetranslation stage and the inkjet print head is positioned outside of anarea to be printed on the substrate.
 8. A method of inkjet printingcomprising monitoring the position of a translation stage arranged toprovide relative movement between a substrate to be printed and aninkjet print head, and controlling the provision of drive signalsarranged to cause ejection of one or more droplets of material from anozzle of the inkjet print head in dependence upon the monitoredposition of the translation stage.
 9. A method as claimed in claim 8,wherein the translation stage is arranged to provide movement of thesubstrate relative to the inkjet print head.
 10. A method as claimed inclaim 8 or 9, comprising generating an encoder signal having a frequencydependent upon the speed of movement of the translation stage and usingthe encoder signals to control the provision of the drive signals.
 11. Amethod as claimed in claim 10, comprising using an optical encoder togenerate the encoder signal.
 12. A method as claimed in claim 8 or 9wherein the encoder signal is arranged to control the timing of theprovision of the drive signals to the inkjet print during translation ofthe substrate relative to the head corresponding to a spatial resolutionin the range of from about 0.1 to about 10 microns between twosuccessive droplets deposited from the inkjet head.
 13. A method asclaimed in claim 12 wherein the timing of the provision of the drivesignals provides about 0.2 microns of spatial resolution between twosuccessive droplets deposited from the inkjet head.
 14. A method asclaimed in any one of claims 8 to 13, comprising selecting a clocksignal from a clock source for controlling the provision of the drivesignals to the inkjet print head when there is no movement of thetranslation stage and the inkjet print head is positioned outside of anarea to be printed on the substrate.
 15. A method as claimed in any oneof claims 8 to 14 wherein the substrate is selected to comprise apre-patterned substrate.
 16. A method as claimed in claim 15 wherein thesubstrate is selected to comprise a substrate having an electrodepre-pattern thereon.
 17. A method as claimed in claim 15 wherein thesubstrate is selected to comprise a pre-pattern of wall structuresdefined in a material having a de-wetting characteristic for thematerial.
 18. A method of manufacturing an electronic, opto-electronic,optical or sensor device comprising a method as claimed in any one ofclaims 8 to
 17. 19. An electronic, opto-electronic, optical or sensordevice manufactured using an ink-jet machine as claimed in any one ofclaims 1 to 7 or a method as claimed in any one of claims 8 to 18.